1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic memory device.
2. Description of the Related Art
Recently, hard disk drives (HDD) are increasingly required to be mass storage devices. In order to satisfy such a requirement, Thermally-Assisted Magnetic Recording (TAMR) is suggested by which data is recorded on a magnetic recording medium while heating the magnetic recording medium by a magnetic head on which a laser light source is mounted.
According to TAMR, as magnetic coercive force can be largely reduced by heating the magnetic recording medium, a material whose magnetic crystalline anisotropy constant Ku is high (hereinafter, referred to as a “high Ku magnetic material” as well) can be used for a magnetic layer of the magnetic recording medium. Thus, grain-size of magnetic materials can be made fine while retaining heat stability, and a surface density of about 1 Tbit/inch2 can be achieved. As the high Ku magnetic material, an ordered alloy or the like such as an L10 FePt alloy, an L10 CoPt alloy or an L11 CoPt alloy is raised.
Further, it is known that oxide such as SiO2 or TiO2, C, BN or the like is added as a material of a grain boundary phase in the magnetic layer in order to separate crystal grains composed of the above described ordered alloy. By forming the magnetic layer to have a granular structure in which crystal grains are separated by a grain boundary phase, exchange couplings between the magnetic grains can be reduced and high medium SNR (signal-noise ratio) can be actualized. For example, Non-Patent Document 1 discloses adding 38% of SiO2 in FePt. Patent Document 1 discloses using Ge oxide in a grain boundary portion of an L10 magnetic layer having a granular structure.
Further, Patent Document 2 discloses that magnetic properties are improved by adding Ag, Au, Ge, Pd or Re in a sputtering target for forming a FePt magnetic layer.
Further, Non-Patent Document 2 discloses a (FePt)Ag—C granular structure as an L10 thin film with high magnetic coercive force.
However, it is still required to improve a recording volume of a magnetic recording medium. Thus, a magnetic recording medium having good electromagnetic transducing properties, in particular, having good SNR is required.